The present invention relates generally to communication satellites, and more particularly, to a traveling wave tube circuit for communication satellites.
Traveling wave tube amplifiers, or traveling wave tubes as they are sometimes referred to, commonly consist of a vacuum tube RF high power amplifier. In most applications for space systems, the high power traveling wave tube amplifier is positioned some distance away from a predistortion linearizer and electronic power conditioner due to the differing operating temperature ranges of these devices. Commonly, the linearizer and power conditioner use solid state components and therefore require a lower operating temperature than the traveling wave tube amplifier. Commonly, an RF interconnecting cable is used to couple the traveling wave tube amplifier and the RF amplifiers and predistortion network. Such a device is shown in prior art FIG. 1 having an RF input 10 coupled to an RF amplifier 12 which in turn is coupled in series with a predistortion network 14. The predistortion network 14 is coupled to a second RF amplifier 16. The second RF amplifier 16 is coupled to the traveling wave tube amplifier 18 by an RF connecting cable 20. The RF amplifier 12, predistortion network 14 and RF amplifier 16 are located in a low temperature zone 22. The traveling wave tube 18 is positioned in a high temperature zone 24.
One problem with such a design is that the RF connecting cable 20 must be accounted for when performing an RF alignment of the linearizer with the traveling wave tube amplifier 18. When the alignment is completed with a specific cable length, any changes to the cable length may change the characteristics of the circuit and therefore the alignment process needs to be repeated.
Another drawback to the system is that the predistortion network is typically comprised of field effect transistors (FETs). These devices have limited operating range for reliable operation.
It would therefore be desirable to provide a traveling wave tube amplifier and predistortion network circuit integrated as a single unit that does not require alignment if the cable length is changed.
It would therefore be desirable to provide an improved traveling wave tube amplifier circuit that allows design flexibility for the spacecraft. It is a further object of the invention to provide a passive linearizer capable of operating at high temperatures to eliminate the effect of the RF connecting cable on the design of the circuit.
In one aspect of the invention, a traveling wave tube amplifier assembly has a traveling wave tube, a predistortion network coupled to the traveling wave tube and physically coupled to the traveling wave tube. An amplifier is separated from the traveling wave tube and the predistortion network by a connecting cable coupled to the amplifier and the predistortion network. In a preferred embodiment of the invention, the predistortion network and traveling wave tube are located in a high temperature zone and the RF amplifier is located in a lower temperature zone than the high temperature zone.
One advantage of the invention is that the cable length may be changed to accommodate various designs process without having to perform another alignment process.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.